Make it possible to specify rule name with '@' prefix to the 'make' rule,

just like for 'notfile' rule. Using rule name without '@' still works
for backward compatibility.


[SVN r33632]

tools/build

@@ -1 +1 @@
-Subproject commit 1982d2c88396d4721e28a5881647d7f53a229ea1
+Subproject commit 5647da05dc5997bf218e0214ab94fb56b84d8ca1